Hi Steve,
We tried to reproduce this in V5.1 by just implement TabbedMDIManager with the GridControl, but could not get this issue. Maybe I am not following the steps that you are doing. Attached sample working fine here. Can you post a small sample showing this problem or tell us how to see it in the Browser sample/Attached sample?
Here is a sample for implementing it.
TabbedMDIManagerWithGrid.zipIf you can provide more information, we can try to suggest some solution.
Best regards,
Haneef